Understanding What Does and Doesn’t Drive Muscle Growth
The model of muscle growth is poorly understood by the average person as is, but many professionals don’t come close to understand it either.
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Refeeds are essentially mini diet breaks (Read this diet break article first if you haven’t). However, instead of going to maintenance for weeks at a time, refeeds only last days. Some people also take refeeds into a surplus.
The general idea is that the quick boost in food will boost your metabolism, decrease your hunger/stress hormones, and retain a bit more muscle so you get better dieting results when you return to dieting.
How well does this play out though?
The proposed mechanism behind refeeds is leptin. Leptin is a hormone that regulates your appetite and energy expenditure. It gets released from fat cells, so the more fat you have, the more leptin you produce which equates to more calories burned and less hunger.
Carbohydrates tend to increase leptin more than fat, so refeeds and diet breaks are usually done by primarily increasing carbohydrate intake (36).
For example, Chin Chance et al found 3 days of overfeeding your maintenance by 30% increased leptin. However, when the participants lowered their energy intake, the increase disappeared (1).
So, your appetite doesn’t remain suppressed after a refeed is over because leptin will drop when you go back to a lower energy intake.
Body composition dictates leptin more than acute energy intake, so to get more leptin, you’d have to actually get fatter (2). Even in healthy individuals, a 50% surplus refeed day doesn’t cause them to eat less the next day (3). Leptin adapts too quickly, within 12 hours, so you can’t temporarily eat more food and trick your body into pumping out leptin long term (2,4). In other words, if you want extra fullness from not dieting, you have to restore your non-dieting body.
This is irrespective of the size of the refeed. Hulmi et al found female competitors who gained weight post-show couldn’t fully restore leptin until their fat mass was fully recovered even after taking a 17.5 week maintenance period (7).
Other research confirms this too. The only time people are able to spike leptin strong enough (+40%) to decrease food intake the following day is when participants ate 120 calories per kg of bodyweight (2). That means a 200-pound person would have to refeed with over 10,000 calories.
So the only way refeeds will even put a dent in the following day’s energy intake is by pigging out disproportionately where you’ll also gain noticeable fat overnight. Essentially, you’re taking 4-5 steps back to take 1 step forward.
Other research is even more grim. One study finds a 60% surplus day increases appetite in subsequent days not decreases it (5). This may be psychological, but that also speaks to a detriment of refeeds. The more calories you refeed, the harder it is to get back to dieting especially in beginner dieters. And the less calories you refeed, the less leptin spikes up.
Regardless, you waste extra days where you could’ve made more progress for a minimal leptin spike that disappears when returning to the diet.
It’s a lose-lose situation as far as appetite is concerned.
Some people propose that refeeds will boost your energy expenditure to help with dieting. We know that increasing food boosts your energy expenditure, but is the effects strong enough?
Most certainly not. If that were the case, we’d all be able to eat extra donuts every weekend and lose the same weight as someone who didn’t.
For example, Dirlewanger et al overfed healthy females 40% past their maintenance (6). This was an average of 670 calories. Their leptin levels only increased 28% and their energy expenditure only increased 7%. This leaves 530 calories to be stored, most of which will be fat tissue.
Simply put, you don’t enhance fat loss by eating more for a day. That’s like saying I’ll clean my garage faster tomorrow if I add more stuff to it today. Completely irrational.
Furthermore, McDevitt et al fed lean and obese individuals a 50% surplus for 4 days (8). This would be similar to a short vacation filled with splurging.
Energy Expenditure only increased 7.9%, so that leaves you in a net 42% surplus. It also found that fat balance was the same whether the participants were overfed with carb or fat.
Protein balance increased by 6-10 grams, so miniscule muscle growth likely occurred as expected with any overfeeding. Interestingly, the carb overfeeding group saw an initial drop in protein balance. This indicates if you do a typical refeed of carbs at maintenance for only a couple of days, you’re restoring some glycogen at best, but not gaining any muscle from the refeed.
This all lines up with adaptive thermogenesis research where the downregulation of your non-exercise activity doesn’t fully recover in some people even after a year of maintenance (9). What makes you think you can get some miraculous effects from a weekend refeed?
Refeeds have also been proposed to retain more muscle mass. From all the data I’ve discussed so far, this isn’t the case. At best, you’d reach the same body composition in a longer time frame.
But what if you match for the same time frame and simply adjusted the energy balance? This means you eat even less during your diet days to afford the additional refeed days.
Campbell et al did a study on this with a continuous dieting group against a refeed group who had 2 maintenance days (30). The study concluded the refeed group had better muscle retention, but the study had many flaws including the fact that the refeed group ate a higher average energy balance and overall adherence was poor.
Consequently, a new paper finalized those flaws and more (31). Campbell’s study also doesn’t line up with the rest of the literature and mechanistically, doesn’t make sense. Why would anyone eat even less for 5 days and think 2 maintenance days per week could increase their muscle balance?
The lower your acute energy balance, the worse your muscle balance will be because protein construction decreases while protein breakdown increases (32,33,34). Not to mention IGF-1, a potentially anabolic hormone decreases as well (35).
It’s simply wiser to stay closer to maintenance and diet on those calories continuously. You’ll have a better protein balance for muscle retention and it’s easier to program workouts to match a consistent calorie intake.
Some people do refeeds with the idea that it’ll reduce cortisol (stress hormone) and increase focus so they have less mental strain when returning to the diet.
However, the research disagrees strongly. For starters, fasting increases cortisol, but overall caloric restriction doesn’t, so despite popular belief, dieting isn’t as physiologically stressful as people claim (10). Even with intermittent fasting protocols, your next meal will normalize cortisol.
The only exception to this is male competitors dieting for contest preps. We have 2 case studies that highlights an increase in cortisol late in their prep. Keep in mind, this occurred in dudes who dieted for 6 months straight on poverty calories without a single slip up all the way down under 5% body fat (11,26).
This level extreme doesn’t apply to you.
Even in female competitors prepping for a show, there is no drop in cortisol from dieting (7).
This lines up with the rest of the literature showing cortisol has no change even during very low-calorie diets and sometimes even decreases with fat loss (12,13,14,15).
In fact, as long as your diet doesn’t impact your sleep or appetite, your caloric intake largely doesn’t matter (16).
The diet fatigue/stress that you’re trying to mitigate with refeeds doesn’t objectively exist. Don’t believe me? Look at more research.
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Wadden et al put obese subjects on either a 500 or 1200 calorie diet (17). Despite the 500-calorie group reporting more dizziness and fatigue, both groups rated the same for diet acceptability and disruptiveness. Psychological performance and hunger were the same between groups as well.
In essence, both groups had the same adherence and having higher calories merely increased comfort on a highly unrealistic study design.
In other studies, when the calories in food are unknowingly reduced even to astronomical levels, there is no difference in hunger, fullness, brain power, memory, mood, or reaction time in a variety of subjects (18,19,20).
Even in lean intense soldiers doing vigorous training, there was no difference in mood, mental performance, and reaction time (21).
Ramadan fasting also has no impact on brain function either (22).
Generally, it is around the 24-48 hour mark where symptoms of stress and anger arise (23,24,25). So sure, if you starve yourself and diet like an idiot on a stranded island, of course refeeds will help destress you.
But the idea of increased diet fatigue and stress from a realistic and controlled diet is unsupported. One systematic review found no correlation between energy intake and brain function (27). In fact, there was a trend that long-term dieting improves brain function because once your nutrition becomes a lifestyle, life gets easier.
The answer is quite interesting. It’s the initial adjustment to knowing you’re on a diet.
In a metabolic ward study where lean participants were forced to exercise and diet on a 40% deficit, they had a drop in mood for the first 3 weeks (28). Even with this huge deficit which would cause muscle loss, there was no further change in mood after 3 weeks. Brain function and sleep were fine the whole time also.
With more realistic protocols, it’s plausible to say your mood might dip for a week, maybe two at most. However, long term comfort won’t get better by taking a break or refeed. Your perceived stress only gets better with consistency because your attempted dieting behaviors needs to become your current lifestyle.
This is why dieting stress/fatigue is pretty massive myth. What you think is a spike in stress is temporary perceived discomfort of adjusting to dieting habits similar to adjusting to any lifestyle change (moving, new job, kids, climate, etc).
If you feel too stressed on your current diet, you either need to
If you avoid the above by taking a refeed, you’re not fixing the root problem. You’re delaying the problem and doing so without any temporary relief. A meta-analysis of 10 controlled studies found there’s no difference in psychological stress between dieters who’ve lost weight or dieters who attempted weight loss, but remained at maintenance (29). In other words, any perceived stress during a diet isn’t from physiologically eating fewer calories.
It’s simply from knowing you’re on a diet because humans associate dieting as unpleasant. Nonetheless, if the thought of dieting is going to be uncomfortable anyways, you might as well reap the most results for your efforts and keep going.
Anecdotally, I notice perceived stress is always outweighed by progress. Clients who insist on refeeds, don’t actually destress. They freak out because the scale is more likely to stall or trend up temporarily.
I’ve found many people think they want a refeed, but what they really want is more progress.
I do employ refeeds when clients have a big social event or holiday coming up that’s not frequent like Thanksgiving. This is simply to give them the option of enjoying life more, not to enhance the diet itself in any way.
I tell them, you won’t lose progress by taking a refeed and I encourage you to take it guilt-free if it’s worth it for you. But if you change your mind, you can still stick to the dieting calories, make a bit more progress, and further lock in the habits necessary for the future.
Again, this is infrequent. If you justified a refeed for every social event or stressful day, you’d be yoyo-ing your calories all week and never accumulate meaningful weight loss.
On another note, refeeds are extremely useful for physique competitors to refuel glycogen and increase muscle fullness during peak week (37). This is a noteworthy use of refeeds, but unfortunately contest prep related circumstances don’t apply to most people.
Because of everything mentioned, refeeds are generally overrated. The physiological benefits are clearly unsupported and the little psychological benefits don’t always outweigh the drawbacks.
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